The risk of a major stroke occurring within a week after a minor stroke is substantial, according to a review to be published in the December issue of The Lancet Neurology.

Major strokes are often preceded by so-called "mini-strokes" or transient ischemic attacks (TIA). They cause the same symptoms as a major stroke, including numbness, slurred speech, paralysis on one side of the body, or a sudden headache. But the symptoms last less than a day, which is why they are called "transient."

Nevertheless, the threat of a more serious stroke occurring within 30 days is increased.

Although many studies have looked at the risk of a major stroke after a minor stroke or transient ischemic attack (TIA), results have been conflicting.

Dr Matthew Giles and Professor Peter Rothwell of the Stroke Prevention Research Unit at the University of Oxford, UK, reviewed studies of the risk of stroke within seven days after a TIA to estimate overall stroke risk. The researchers looked at 18 studies that included 10,126 patients.

They found that one in 20 patients who have a TIA will go on to have a stroke within a week.

They also found that the lowest risks of stroke were seen in those patients who had emergency treatment in specialist stroke units for their TIA. The highest risk was in those patients who didn't receive urgent treatment (11 per cent).

The authors say that the individual results of the studies are inconsistent, but the variation can be almost fully explained by differences in study method, setting, and treatment.

The authors say the results of their study support the argument that a TIA is a medical emergency. They say urgent treatment in specialist units, where patients are often prescribed blood thinners and cholesterol-lowering drugs to prevent another stroke, can go far to reduce the risk of subsequent stroke.